How Legal is a Contract Vs Signed Letter Agreement

I would like advice on the following:

A Property owner has signed a Letter of Agreement to promise to enter into a contract of Lease with Person A at a specific date in the future, for five years and for a fixed rent amount every month. The Letter of Agreement is signed by the Property owner and the Person A and also has witness signaturies. It also is nortorised by 'Hand and Seal' by a Lawyer/Attorney of Law.

My question is this: How strong is this signed Letter of Agreement and can it hold up in the court of Law given that a Contract of Lease is not yet signed?
I am afraid that the Property Owner can refuse to sign a Contract of Lease in the future date specified. If they do so, what are the legal consequences? Is signing this Letter of Agreement as strong as signing a Contract of Lease?

A detailed answer or advice is appreciated.
Thanks

did the lessor already occupy the property and begin paying rent?

The Person A (Leasee) has already occupied the building and paying rent.

How does this fact affect the situation?

Thanks

in that case, i would argue that the letter now constitutes their contract.

Hello Attorney,

Thanks for the advice however I would like to add some extra facts if it will in anyway change the advice you have previously given.

* The Letter Agreement states that the Land owner will enter into a Contract of Lease for the future for five years, for example Dec 2011 to Dec 2016.
* The Person A has legal rights to occupy the building at the moment because has an existing sublease agreement. Land Owner signed a contract of Lease with Person Z, who subleases the first floor of the building to Person A. However this current sublease agreement ends 30th Nov 2011. The land owner does not want to extend the lease with Person Z but does promise Person A that they will directly enter a Contract of Lease with them for the first floor of the building when the current sublease contract ends on 30th Nov 2011. Person A wants to ensure that the landowner performs his promise and so Person A and the Landowner sign A Letter Agreement that the Land owner will infact enter into a contract of lease Dec 2011 to Dec 2016.
Given these extra facts, does your answer change Attorney?

P.S by land owner I mean that he also owns the property/building on the land and not just the land, thanks.

Thanks in advance for the advice,

yes, because A was already occupying the property before the letter.

if no contract is executed, A will have to go to court to compel the owner to execute a contract and/or pay damages.